transport across cell membranes

Question 1

What are plasma membranes?

Answer 1

All membranes around and within all cells and cell organelles

Question 2

What is the cell-surface membrane?

Answer 2

Name given to the plasma membrane that surrounds cells and forms and forms a boundary between the cytoplasm and the environment

Question 3

What does the cell-surface membrane control?

Answer 3

Controls the movement of substances in and out of the cell

Question 4

What are the 5 important components of the cell-surface membrane?

Answer 4

Phospholipids
Proteins
Cholesterol
Glycolipids
Glycoproteins

Question 5

Why are phospholipids important components of the cell-surface membrane?

Answer 5

-The hydrophilic heads of both the layers point to the outside of the cell-surface membrane and the hydrophobic tails point to the centre.

Question 6

What kind of material can move through the membrane via the phospholipid portion?

Answer 6

Lipid-soluble material

Question 7

What are the 3 functions of phospholipids in the membrane?

Answer 7

1. Allows lipid-soluble substances to enter and leave the cell
2. Prevents water-soluble substances entering and leaving the cell
3. Makes the membrane flexible and self-sealing

Question 8

How are proteins spread about the cell-surface membrane?

Answer 8

Interspersed

Question 9

What are the functions of proteins that are embedded in the cell-surface membrane?

Answer 9

They give mechanical support to the membrane or as cell receptors for molecules such as hormones

Question 10

Which proteins span the cell-surface membrane?

Answer 10

Channel proteins and carrier proteins

Question 11

What are the 6 different functions of proteins in the membrane?

Answer 11

Provide structural support

Act as channels transporting water-soluble substances across the membrane

Allow active transport across the membrane through carrier proteins

Form cell-surface receptors for identifying cells

Help cells adhere together

Act as receptors for molecules such as hormones

Question 12

What are glycolipids made up of?

Answer 12

A carbohydrate covalently bonded with a lipid

Question 13

How far does the carbohydrate portion of a glycolipid extend?

Answer 13

From the phospholipid bilayer into the watery environment outside the cell where it acts as a cell-surface receptor for specific chemicals.

Question 13

What are the 3 functions of glycolipids in the membrane?

Answer 13

Act as recognition sites

Help maintain the stability of the membrane

Help cells attach to one another and so form tissues

Question 14

What do glycoproteins act as?

Answer 14

Cell surface receptors, specifically for hormones and neurotransmitters

Question 15

What are the 3 functions of glycoproteins in the membrane?

Answer 15

Act as recognition sites

Help cells attach to one another and so form tissues

Allows cells to recognise one another, for example lymphocytes can recognise an organisms own cells

Question 16

What role do membranes play in organelles like mitochondria and chloroplasts?

Answer 16

Separate organelles from cytoplasm for specific metabolic reactions

Question 17

What internal transport system is provided by membranes within cells?

Answer 17

Endoplasmic reticulum

Question 18

How do membranes isolate potentially damaging enzymes?

Answer 18

By containing lysosomes

Question 19

What surfaces do membranes provide for cellular reactions?

Answer 19

Surfaces for reactions such as protein synthesis

Question 20

Fill in the blank: The permeability of the cell-surface membrane is affected by the _______.

Answer 20

Temperature, pH,

Question 21

What are the three main reasons most molecules do not freely diffuse across the cell-surface membrane?

Answer 21

1. Not soluble in lipids
2. Too large to pass through channels
3. Same charge as the protein channels

These factors hinder the ability of molecules to cross the membrane.

Question 22

What is the fluid-mosaic model of the cell-surface membrane?

Answer 22

A model describing the flexible structure of the membrane with varying protein shapes and sizes

‘Fluid’ refers to the movement of phospholipids; ‘mosaic’ refers to the diverse proteins embedded.

Question 23

Why is the term ‘fluid’ used in the fluid-mosaic model?

Answer 23

Individual phospholipid molecules can move relative to one another

This movement allows the membrane to be flexible and change shape.

Question 24

What is the function of glycoproteins in the cell-surface membrane?

Answer 24

Act as recognition sites for chemicals, e.g., hormones

Question 25

What role does cholesterol play in the cell-surface membrane?

Answer 25

Adds strength to the membrane ## Footnote Cholesterol helps maintain membrane integrity and fluidity.

Question 26

What is the definition of diffusion?

Answer 26

The net movement of molecules or ions from a region where they are more highly concentrated to one where their concentration is lower until evenly distributed.

Question 27

What type of transport is diffusion classified as?

Answer 27

Passive transport.

Question 28

What energy source is necessary for diffusion?

Answer 28

No external source of energy is required; the motion comes from the kinetic energy of the particles.

Question 29

What are the characteristics of particles in diffusion?

Answer 29

Particles are constantly in motion, with random movement and no set pattern.

Question 30

Which molecules can easily diffuse across cell membranes?

Answer 30

Small, non-polar molecules such as oxygen and carbon dioxide.

Question 31

What is facilitated diffusion?

Answer 31

A passive process that helps charged ions and polar molecules diffuse across membranes via transmembrane channels and carriers.

Question 32

What is the main difference between diffusion and facilitated diffusion?

Answer 32

Facilitated diffusion occurs at specific points on the plasma membrane and involves protein channels and carriers.

Question 33

What type of molecules do not diffuse easily across plasma membranes?

Answer 33

Charged ions and polar molecules.

Question 34

What is the role of transmembrane proteins in facilitated diffusion?

Answer 34

They facilitate the movement of molecules that cannot easily pass through the membrane.

Question 35

True or False: Diffusion requires an external input of ATP.

Answer 35

False.

Question 36

Fill in the blank: Diffusion occurs down a _______.

Answer 36

concentration gradient.

Question 37

What happens to particles concentrated in one part of a closed vessel during diffusion?

Answer 37

They distribute themselves evenly throughout the vessel.

Question 38

What is the kinetic energy's role in diffusion?

Answer 38

It causes particles to move randomly, allowing diffusion to occur.

Question 39

What are the two types of proteins involved in facilitated diffusion?

Answer 39

* Protein channels * Carrier proteins

Question 40

What is a key hint to remember about diffusion?

Answer 40

Diffusion is the net movement of particles; more move in one direction than in another due to concentration differences.

Question 41

Fill in the blank: Diffusion only occurs between different concentrations of the _______.

Answer 41

same substance.

Question 42

What are protein channels?

Answer 42

Proteins that form water-filled openings in the membrane, allowing specific water-soluble ions to pass through ## Footnote They are selective, opening only in the presence of specific ions.

Question 43

How do protein channels control ion movement?

Answer 43

They remain closed if the specific ion is not present, controlling the entry and exit of ions ## Footnote Ions bind to the channel, causing it to close to one side of the membrane.

Question 44

What is the role of hydrophilic channels?

Answer 44

They facilitate the passage of water-soluble ions through the membrane ## Footnote Hydrophilic properties attract water and ions.

Question 45

What are carrier proteins?

Answer 45

Proteins that span the plasma membrane and assist in the facilitated diffusion of molecules ## Footnote They change shape to transport specific molecules.

Question 46

How do carrier proteins facilitate the transport of glucose?

Answer 46

When glucose binds to the carrier protein, it causes the protein to change shape and release glucose inside the membrane ## Footnote This process does not require external energy.

Question 47

What is facilitated diffusion?

Answer 47

A process where molecules move from an area of high concentration to an area of low concentration without energy ## Footnote Utilizes the kinetic energy of the molecules.

Question 48

Fill in the blank: Protein channels are _______ to specific ions.

Answer 48

selective

Question 49

True or False: Carrier proteins require external energy to transport molecules.

Answer 49

False ## Footnote They operate using the kinetic energy of the molecules.

Question 50

What triggers the opening of a protein channel?

Answer 50

The presence of a specific ion ## Footnote This selectivity ensures proper ion regulation.

Question 51

What happens to a carrier protein when a specific molecule binds to it?

Answer 51

It changes shape to release the molecule inside the membrane ## Footnote This is a key mechanism in facilitated diffusion.